1. Field of the Invention
This invention relates to a gas-insulated switching apparatus having interrupters disconnecting switches, buses and the like, and provided with line portions incorporated within ground potential metallic containers in which insulating gas is sealed.
2. Description of the Prior Art
For the purpose of limiting the site area required for substations or switching stations and for ease of designing salt-resist structures for use in coastal districts, a large number of gas-insulated switching apparatus has hitherto been utilized, which incorporate a series of device components such as interrupters, disconnecting switches and buses within grounded metal containers filled with insulating gas such as sulfur hexafluoride (SF.sub.6) gas.
Disconnecting switches used for such apparatus in substations are operated in order to disconnect in-house devices from power system, or to perform changeover of in-house circuits. Switching operations of the disconnecting switches are carried out during the period while the adjacent interrupters are opened. The disconnecting switches switch small charging currents on short-distance lines connected to the adjacent interrupters in a substation.
When a disconnecting switch interrupts a charging current, a large number of restrikings occur, and these restrikings can cause grounding flash-over the disconnecting switch, as explained in IEEE Transactions on Power Apparatus and Systems, Vol. PAS-101, No. 10, pp. 3593-3602 and Vol. PAS-100, No. 6, pp. 2726-2732.
Many disconnecting switches employed in a substation are all identical in ratings when they are applied into identical system voltages, however, only specific disconnecting switches cause grounding faults. Such specific disconnecting switches may not readily be distinguished from healthy disconnecting switches which do not cause grounding faults because no difference can be seen when they are compared with an individual withstanding voltage test procedure. Further, phenomena have been observed whereby only disconnecting switches which are installed at the specific portions in a gas-insulated switching apparatus tend to cause grounding flash-over. The causes for such phenomena have not been recognized despite various experiments and studies.